Medium-voltage switching devices are equipped with so-called pole parts in which vacuum interrupt chambers, which are the actual switching elements, are installed, or are encapsulated in the situation that is relevant to the present disclosure. Pole parts have two fixed-position connecting pieces, by means of which the switching device is connected to further components in the switchgear assembly. The fixed-position connecting pieces are connected to the supply lines to the vacuum interrupt chamber, within the pole part. On one side, i.e., the fixed contact side, the connection is rigid, and is produced before the encapsulation of the pole part. On the other side, i.e., the switching contact side, the fixed-position connecting piece of the pole part is connected to the moving supply line of the vacuum interrupt chamber so as to allow relative movement of the moving supply line. This latter connection may be produced in the form of a multicontact system before encapsulation, or else in the form of a current ribbon after encapsulation.
It is known for encapsulated pole parts to be produced from epoxy resin using a pressure gelation process. The epoxy-resin pole part is used to increase the external dielectric strength of the vacuum interrupt chamber, and carries out mechanical functions. It is likewise known for pole parts to be produced using an injection-molding process, in which case thermoplastics can be used, in addition to thermosetting plastic materials, as is known from DE 10 2005 039 555 A1.
In contrast to the pressure gelation process, mold internal pressures occur in the injection-molding process and are more than 100 bar, for example, approximately 300-400 bar is of mold internal pressures are known to occur for conventional injection molding.
The injection-molding process involves a considerably reduced cycle time and a simplified production process, and ensures the mechanical and dielectric characteristics.
In all of the already known methods for production of encapsulated pole parts, the vacuum interrupt chamber is encapsulated completely in the insulating material, except for the end surface on the switching contact side. The free space which is required for the switching function below the vacuum interrupt chamber is achieved by means of a so-called mold core, which is sealed on the end surface of the cover of the vacuum interrupt chamber, and which prevents the ingress of liquid insulating material during the encapsulation process.
During the spraying process in injection molding, forces act on the vacuum interrupt chamber. Locally, such forces first of all affect the tool internal pressure that occurs, and can lead to local deformation of the steel covers of the vacuum interrupt chambers. However, the filling process also results in overall forces on the vacuum interrupt chamber. In the case of filling from the fixed-contact side, an axial force acts on the vacuum interrupt chamber, which can lead to the upper and lower chamber covers being forced inward when a fixed mold core is used.
In an attempt to ensure that the vacuum interrupt chamber will withstand these forces without being damaged, it has been proposed for the vacuum interrupt chamber to be reinforced by wall-thickness inserts in the stainless-steel covers, by external caps or by specifically shaped ceramic parts (application No. 102006041149.8-34).
The proposed reinforcement measures for the vacuum interrupt chamber, however, involve processes with high costs.